by 
The Curious Bag
-
Valve cover breathers are generally used with older engines and act as vents to release blowby-induced pressure in an engine's crankcase. Though modern engines take this venting one step further by creating a vacuum in the system, the principle remains the same.
Blow-By
Since even the best piston rings only contain about 96 to 98 percent of the gases produced by the exploding air-fuel mixture, some will always leak past and into the crankcase. This leakage is called "blowby."
Crankcase Pressure
As well-tuned engines can produce more than 200 pounds per square inch (psi) of cylinder pressure, blowby could easily increase pressure in a sealed crankcase to more than 10 psi in a matter of moments, increasing almost exponentially as the engine continues to run.
Oiling Failure
Oil pumps generally deliver pressure in the 20 to 70 psi range, so ambient pressure in the engine can cause oil starvation if it exceeds the oil pump's pressure.
Gasket Failure
Excess positive pressure can cause gaskets to blow out. Valve covers, oil pan and timing cover gaskets are usually the first to go.
Positive Evacuation
Modern engines use either an intake pressure siphon or stand-alone vacuum pump to keep the crankcase at well below atmospheric pressure.
Source:
Resource:
How a Dry-Sump System Works (Video)
RELATED QUESTIONS
Copyright 2023, Wired Ivy, LLC